Starfleet commissioned the brilliant holo-programmer DoctorLewis Zimmerman at the Jupiter Station Holoprogramming Center as the embodiment of modern medicine. The EMH Mark I was first activated in 2371, and was programmed with over five million possible treatments from the collective information of two thousand medical references and the experience of 47 individual medical officers. The EMH was also supplemented with contingency programs and adaptive programs to learn while serving as a supplement of a normal medical staff in cases of emergency. It contained fifty million gigaquads of computer memory, which was "considerably more than most highly developed humanoid brains." (VOY: "Life Line")

This bit of information was seen on a small viewscreen detailing Zimmerman's life and work history in the above-mentioned episode.

Dr. Zimmerman, proud of his achievement, decided to program the EMH with both his physical, and most notably, psychological characteristics. Unfortunately, Dr. Zimmerman did not take into account that his own personality resulted in a poor bedside manner for a medical doctor. The resulting hologram was arrogant and irritable, and as a result was poorly received by many Starfleet doctors. This, in turn, spawned nicknames like "Emergency Medical Hotheads" and "Extremely Marginal Housecalls." (VOY: "Life Line") Some biological Starfleet doctors even went so far as to object to the use of the EMH. DoctorBeverly Crusher swore that she would never use one, although she was forced to do so in order to create a distraction while the Borg tried to assimilate the USS Enterprise-E, allowing her, her medical staff, and her patients, notably Lily Sloane, to escape from sickbay. (Star Trek: First Contact)

Eventually it was concluded that the EMH Mark I was defective, and they were retired from the medical corps. While an ashamed Dr. Zimmerman tried to have them decommissioned, Starfleet reassigned them to scrub plasma conduits on waste transfer barges. Later, the Mark Is were also deployed in other menial tasks, like dilithiummining.

Most notably The Doctor, a Mark I serving on the USS Voyager, ran almost continuously for years and was forced to expand his programming extensively to keep up. This EMH originally objected to being the replacement for the entire medical staff, as the EMH program was only meant to function for a maximum of 1,500 hours (62.5 days); after this time, memory degradation would occur. Fortunately, with the help of his colleagues, his program was altered to overcome this shortcoming. (VOY: "The Swarm")

To address the flaws in the EMH Mark I, Dr. Zimmerman began work on the Mark II, a prototype of which was finished in time to be included in the sickbay of the USS Prometheus in 2374.

While the Mark I's outward appearance was a copy of its inventor, a disillusioned Dr. Zimmerman changed the outward appearance of the Mark II. Furthermore, the patterns of behavior of the following versions were designed to be more pleasant and courteous. To achieve this, Zimmerman initially tried to improve on the programming of the Mark I, but eventually decided to create the Mark II from scratch. In addition to that, new ship designs like the USS Prometheus enabled full mobility for the EMH, as the whole ship was outfitted with holographic projectors.

By 2377, the Mark II had been replaced by a Mark III, followed by a Mark IV. (VOY: "Life Line")

Neither the Mark III or Mark IV programs were shown on-screen, nor was it revealed what happened to the Mark II.

Several EMH Mark Is mining dilithium

By 2378, the Mark I programs were reconfigured to work at a Federation mining colony in replacement of other forms of labor. These programs, having been reassigned to their new function, were able to obtain bootlegged copies of the holonovelPhotons Be Free and view them. One of the EMH miners found the holonovel "provocative". (VOY: "Author, Author")

The fact that the reconfigured Mark Is could view holonovels suggests that they retained at least some level of sentience left over from their original medical programming.

After the EMH Mark II supplanted the "inferior" Mark I, the only remaining versions to fulfill their original programming were aboard the USS Voyager and the USS Equinox, which were both stranded in the Delta Quadrant and had to implement the emergency holograms for extended periods of time. However, a notable caveat was that the crew of the Equinox deleted their EMH's ethical subroutines in order to allow him to act contrary to the Hippocratic Oath. In 2376, the Equinox EMH was deleted while in Voyager's database, leaving Voyager's program, "The Doctor", as the only Mark I still operating as an EMH. (VOY: "Equinox", "Equinox, Part II")

Voyager's EMH (The Doctor) developed a distinct personality over the ship's seven-year-long journey to the Alpha Quadrant. Despite this, The Doctor was not granted the rights of a living person by a Federation Arbiter, although he did determine that The Doctor fulfilled the requirements of an artist under the law. The Arbiter did, however, encourage The Doctor to pursue recognition as a sentient being at a later point in time. (VOY: "Author, Author")

When The Doctor was sent in a holographic data stream to contact the USS Prometheus, he found the starship in the hands of Romulans, who had killed the Starfleet crew and captured the ship. The Doctor activated the ship's EMH, a Mark II, to help him recapture the ship, although the Mark II initially preferred to just deactivate and wait for rescue, and then treated The Doctor as inferior despite the latter's vastly superior life experiences. The Doctor ultimately persuaded the Mark II to take action and help him. They planned to disable the Romulans by venting an anesthetic gas, but The Doctor was captured by the Romulans when he attempted to reach the environmental controls on the bridge. During The Doctor's interrogation, the Mark II simulated a bio-hazard, opening the vents which released the gas, knocking out the Romulans. The Doctor and the Mark II successfully fought off Romulan warbirds using the ship's experimental weapons systems, returned the ship into Starfleet's hands, and informed Starfleet that Voyager was in the Delta Quadrant. (VOY: "Message in a Bottle")

The EMH was a holographic simulation of a Human, but with no internal organs beneath the apparent surface to conserve computer power. EMHs were not equipped with reproductive organs. The Doctor, however, wrote additional routines into his holomatrix to facilitate romantic endeavors and has also had several relationships, one of which inexplicably resulted in a son. (VOY: "Message in a Bottle", "Blink of an Eye")

Magnetic containment fields allowed the EMH to interact with physical objects. These force fields moved as the EMH moved to create the appearance of solid matter. The containment fields could be shut off, allowing objects and people to pass through them – an EMH's cohesion could range from solid to intangible. (VOY: "Phage") When OHDs and magnetic field generators were added to other parts of a ship, they allowed the hologram to leave sickbay (as in more advanced Starfleet ships or modified configurations). Without these additional projectors, the EMH could only function in sickbay and the holodeck.

The USS Voyager also discovered the 29th century mobile emitter technology which, when attached to the EMH and its program transferred to emitter, allowed the EMH to roam freely on board ship, shuttles, or even planetary surfaces. This allowed the EMH to act as a medical aid during away missions. However, damage to the emitter posed a risk of damage or even deletion of the EMH.

When he was first activated, the Voyager EMH apparently did not have the ability to deactivate himself after he finished his duties. However, he was later given that ability by issuing computer command "Override Command 1-EMH-Alpha; End Program". (VOY: "Jetrel") The Mark II apparently had this ability as part of his programming. (VOY: "Message in a Bottle")

While not designed to act as ship's counselor, the EMH had been programed with some psychological knowledge. (VOY: "Darkling")

In Star Trek Online's Federation tutorial, players encounter a new version of the Emergency Medical Hologram (EMH Mark VI) serving aboard the USS Khitomer. Resembling a Vulcan with silver hair, this EMH, in dialogue released on YouTube but not included in game, claims to have a "personality matrix [that] combines qualities of more than twenty physicians, scientists, and counselors - including AdmiralBeverly Crusher of Starfleet Medical, AmbassadorSpock, and Ghee P'Trell of Andoria." He is voiced by Zachary Quinto. [1] Also in Star Trek Online, Emergency Medical Holograms, alongside the new Emergency Engineering Holograms and Emergency Security Holograms, can be acquired as Duty Officers. [2]